In this case, an expert relied upon a number of documents supporting the plaintiff’s claim and which lay the foundation for his expert opinion, however those supporting documents were not adduced in evidence.
The plaintiff and the defendant entered a contract, pursuant to which the defendant was to carry out works to supply and install a soil mixing system. The defendant was in breach of certain terms of the contract.
An entry of default judgment was issued in plaintiff’s favour. Pursuant to O 13, r 3 of the Supreme Court Rules 1971 (WA), the plaintiff subsequently sought an assessment of damages. The plaintiff was in liquidation and had subrogated its rights in relation to its claim and the sum indemnified under its relevant insurance policy to its insurers.
The plaintiff relied upon the expert opinion of Mr McW, a loss adjustor in the construction field, to establish that what had been paid to the plaintiff under the policy was as a result of the loss caused by the defendant’s breach of contract.
In Mr McW’s affidavit, he stated that the payments recommended by him were properly supported by the information he obtained during his investigations, and that the amounts claimed were reasonably incurred in connection with the defendant’s breach of contract.
While the court accepted that Mr McW was appropriately qualified to give the opinion he, none of the supporting material (e.g., invoices, site diaries, correspondence from the plaintiff to Mr McW in which explanations were given for the rectification works, other expert opinions on which Mr M relied, or any other material) was adduced.
The court emphasised that for an evidence of an opinion to be admissible, it must be based on other admissible evidence, and that evidence must ordinarily be adduced.
Mr McW estimated that it would take 50 hours to provide the source information for his reports, composed of more than 1070 documents, with more than 10,000 pages.
The plaintiff argued that the reports of Mr McW should be admitted pursuant to s 27B of the Evidence Act 1906 (WA) (the Act), which states:
If a court is satisfied that particular evidence that a party to a proceeding proposes to adduce is so voluminous or complex that it would be difficult to assess or comprehend it if it were adduced in narrative form, the court may direct the party to adduce the evidence in another form, including in the form of a chart, summary or other explanatory document.
The plaintiff relied upon Noske v The Queen  WASC 56 (Noske), which cited R v Fysh  NSWSC 1266 (Fysh) in support of this argument.
In Fysh, the court ruled that an expert could give evidence as to the fact that certain information did not appear in documents, even though this was not an issue which required specialised knowledge.
However, in both Noske and Fysh, the evidence relied upon by the expert had been collated and provided to the other party to the proceedings. In doing so, the other party could check the source documents and test the evidence if it did not support the evidence given by the expert.
In the present case, the source documents had not been provided to the other side. The defendant, through the Liquidator, had been made aware of the plaintiff’s claim and indicated it did not seek to be heard.
For that reason, Forrester J was satisfied that the evidentiary material underpinning Mr McW’s quantification of the plaintiff’s claim and his expert opinion regarding it was so voluminous and complex it would be difficult to assess or comprehend. 
Mr McW’s reports constituted explanatory documents which provided an adequate summary of the evidentiary material relied upon, and comprehensively explained the reasoning process behind his expert opinion. 
In these circumstances and pursuant to s 27B of the Act, the court considered it appropriate to admit parts of Mr McW’s reports which summarised the underlying evidentiary material and which lay the foundation for his expert opinion. 
Relying solely on the expert opinions of Mr McW in making out its claim, and on the basis the plaintiff provided no other evidence upon which the court could be satisfied, to the required standard, that the plaintiff suffered the loss claimed, the plaintiff’s claim was allowed in part.
· Ordinarily, for opinion evidence to be admissible, any evidence underpinning the opinion must also be adduced.
· Evidence legislation provides an exception for voluminous or complex material. Section 50 of the Evidence Act 1995 (Cth) contains a similar provision to that in s 27B of the Evidence Act 1906 (WA) for voluminous or complex documents.
· Where an expert relies on voluminous or complex material to underpin their opinion, the expert should provide an adequate summary of that material and explain their process of reasoning based on that material.